Needle/syringe exchange program (SEPs) have been implemented to slow the spread of HIV-1 infection among injection drug users (IDUs). Their benefits to program participants has been repeatedly demonstrated. However, it is uncertain if benefits accrue to IDUs who do not actively use the exchange. The goals of this application are to determine if there is a diffusion of benefit beyond direct SEP participants. Three SEPs - Hartford, Ct, Oakland, Ca, and Chicago, IL - will be the sites at which these evaluations take place. The diffusion will be analyzed using measures of direct benefit (syringe, tracking and testing) and measures of indirect benefits (changes in HIV-related risk reduction knowledge, risky injection practices, and use of non-exchange services). The direct diffusion will be measured using marked syringes that will permit determination of the circulation times and HIV prevalence of syringes, which are associated with the risk of transmitting HIV. Indirect diffusion will be measured by quantifying specific AIDS knowledge, risky injection practices, and use of referral to drug treatment, medical, or social services before and after interventions that involve the distribution of relevant printed material by the SEPs. The applicants aim to achieve the following specific aims: 1) In the three locations where SEPs are active, ethnographic studies will identify and recruit individuals and networks of IDUs based on their level of program participation. 2) The role of SEPs in directly decreasing HIV transmission will be assessed using a modified syringe tracking and testing system. 3) The role of SEPs in disseminating accurate, usable prevention messages will be determined. One aspect focuses on diffusion of new HIV-related knowledge; a second focuses on diffusion of behavior change. 4) The role of SEPs in providing non-exchange services will be studied, and the ability of SEPs to increase service use by participants, indirect participants, and non-participants will be determined. This study involves a number of distinct but interrelated components. Once the Specific Aim #1 is achieved -- individuals and networks are recruited -- he work to achieve Aims #2-4 is undertaken concomitantly and staged over 3 years. A multidisciplinary team of molecular and statistical epidemiologists and ethnographers has been assembled to accomplish these tasks.